History
The development of the first production Curtiss P-40 Warhawk was initiated by Curtiss P-36 Hawk with a radial, air-cooled engine. The US Army Air Corps determined that the P-36 was already outdated and inferior to more modern European designs in early 1937, and the USAAC needed more modern fighters to expand its force.
In 1937, a P-36 was ordered to be modified with an Allison V-1710-11 inline engine and turbo-supercharger as an XP-37 prototype. In 1938, another prototype was ordered and modified with a V-1710-21 and a more reliable supercharger as a YP-37 prototype. Both prototypes had severe supercharger and visibility problems, as their cockpit had to extend back towards the tail to make room for the massive supercharger. The decision was made to cancel the development of production P-37.
Instead, the other decision was made to move to a straightforward, simple conversion of the P-36 without a turbo-supercharger. The 10th-built P-36A was selected and installed with a 1,150-hp V-1710-19 engine and a liquid-cooled engine with integral supercharging. This aircraft’s cockpit did not have to move back. Only the fuselage was modified with some changes to give room for the Allison engine; carburetor intake for the single-stage supercharger was installed in the upper nose between the two nose guns; an oil cooler was mounted underneath the nose; and the radiator was moved to the ventral position just aft of the wing. This conversion project gave a new designation for the fighter prototype - XP-40.
On October 14, 1938, the prototype XP-40 flew on its first flight in Buffalo. The flight tests showed the aircraft was capable of flying at a speed of 300 mph. Unsatisfied with the tests, the aircraft was taken and evaluated in a NACA wind tunnel to identify solutions. The Curtiss engineers worked on the XP-40 to improve the speed by moving the
radiator forward in steps and making minor tweaks, such as redesigned landing gear. The modified XP-40 flew again for the flight tests. Further tests proved the aircraft was capable of flying at an average speed of 354 mph and could reach a top speed of 366 mph.
In April 1939, the USAAC received reports regarding European air forces with their new, high-speed, inline-engined fighters ready for combat operations. This prompted the USAAC to accept the XP-40 as an entry for the production P-40, and the USAAC placed the largest fighter order, 524 P-40s.
The initial production P-40, or P-40-CU, was nearly identical to the XP-40 but with a 1,040-hp V-1710-33 and one .30 cal machine gun in each wing. The P-40-CU was built with flush riveting to reduce drag and designated as the Model 81 to differentiate itself from the Model 75 of the P-36 Hawk. As an initial configuration, the P-40 was armed with two .50 cal nose guns and two .30 cal wing guns and was not fitted with bulletproof windshields, armor, and self-sealing fuel tanks.
The P-40-CU (serial number 39-156) made its first flight on April 4, 1940. It reached 15,000 feet in 5.2 minutes and a maximum speed of 357 mph at that altitude. The P-40-CU was perceived as a pure pursuit aircraft and was agile at low and medium altitudes but suffered from a lack of potent power at higher altitudes due to the single-stage, single-speed supercharger.
The P-40-CU fighters were first delivered to the USAAC units in June 1940. The first three of the P-40-CUs were used for service testing. The 33rd, 35th, and 36th Pursuit Squadrons of the 8th Pursuit Group, based at Langley Field, Virginia, were among the first units to acquire these P-40-CUs. In addition, the 55th, 77th, and 79th Pursuit squadrons of the 20th Pursuit Group at Selfridge Field, Michigan, received the new P-40-CUs. The P-40-CUs were applied with full prewar camouflage of olive drab on the top and gray on the undersides, and the standard rudder stripes and star insignia were applied to both wings.
A batch of 200 P-40-CUs was delivered to the USAAC units and completed by October 15, 1940. Additional 140 French-ordered P-40-CUs (H-81As) were routed to France but were taken over by the Royal Air Force in September of 1940 as a consequence of the French Armistice. Those aircraft were designated Tomahawk Mk. I.
These P-40-CUs in the USAAC service were not combat-ready and were restricted from combat duty because of a lack of heavier armament and armor. Only the Tomahawk Mk. Is of the RAF had seen their combat action in North Africa.
